1. Field of the Invention
The present invention pertains to a cermet suitably used for manufacturing cutting tools used in interrupted cutting operations such as milling operations.
2. Prior Art
The cermet was the material for cutting tools developed by Ford Motors Company in 1959, and had a composition of TiC-Ni-Mo(Mo.sub.2 C). The discovery of the Ford Motors Company was that the addition of molybdenum (Mo) or molybdenum carbide (Mo.sub.2 C) improved the degree of sintering and the alloy structure of TiC-Ni cermet to thereby enhance its strength. A further improved cermet which includes titanium nitride (TiN) has been developed nowadays, but the addition of molybdenum or molybdenum carbide has still been considered to be indispensable.
One of the inventors has presented his report entitled "THE REACTION OCCURRING DURING SINTERING AND CHARACTERISTICS OF TiC-20%TiN-15%WC-10%TaC-9%Mo-5.5%Ni-11%Co CERMET" at 10th Planesee Seminar (June 1st to 5th, 1981, Routte, Austria). Japanese Patent Laid-Open (18-Months Publication) No. 50-102508 and U.S. Pat. No. 4,046,517 describe the above TiC-TiN-WC-TaC-Mo-Co cermet. The TiC-TiN-WC-TaC-Mo-Co cermet exhibits superior wear resistance in turning operation of steel, but is susceptible to fracturing during interrupted cutting operations such as milling operations.
Therefore, the inventors have made a further study and found that a cermet free of molybdenum or molybdenum carbide is less susceptible to fracturing, as disclosed in Japanese Patent Application Laid-Open No. 60-221547. However, even such a cermet is still insufficient in toughness when used as cutting tools for interrupted cutting operations.